Axle driving apparatus

ABSTRACT

An axle driving apparatus consisting of a housing for compactly housing inner portions of axles, a hydrostatic transmission, and a transmitting mechanism for transmitting power to the axles from an output shaft of the hydrostatic transmission. The housing is partitioned by an internal wall into a chamber containing the hydrostatic transmission and a chamber containing the other transmitting mechanisms. The housing is filled with oil in common with both chambers. A trunnion for changing the output rotation of the hydrostatic transmission is disposed in parallel to the axles. A shock absorber is provided to prevent abrupt speed change. A differential locking device is attached to the differential gear to thereby improve the straightforward running capacity of the vehicle.

FIELD OF THE INVENTION

The present invention relates to an axle driving apparatus for improvingthe straightforward running capacity of a vehicle on a muddy road or thelike, and more particularly to an axle driving apparatus which isintegrally provided with a hydrostatic transmission (hereinafterreferred to as the HST); axles; a power transmitting mechanism, whichcan easily change the speed of the HST; an oil reservoir, which canabsorb an increase in the volume of oil due to an increase in thetemperature of the HST; and a differential locking device, all of whichare provided in a single housing.

BACKGROUND OF THE INVENTION

Conventionally, an axle driving apparatus consists of a housing for anHST, axles and a power transmitting device for interconnecting the HSTand axles. On the center section of the HST is disposed a hydraulicpump, provided with a vertical input shaft, and a hydraulic motor,provided with a horizontal output shaft. A plurality of pistons aredisposed in the hydraulic pump cylinder block. The heads of the pistonsabut against a movable swash plate. Changing the angle of the movableswash plate changes the pump capacity so as to increase or decrease thenumber of rotations of the hydraulic motor. The movable swash plate isslanted, thereby enabling the speed of the HST to be changed byrotatably operating trunnions supported in the housing. Each trunnion isdisposed on a longitudinally slanted axis of the swash plate, asdisclosed in U.S. Pat. No. 5,456,068, for example.

A speed change controller, such as a pedal or a lever, which is providedon the vehicle can be operated normally longitudinally thereof so thatits motion can be transmitted to a control arm of the axle drivingapparatus through a link mechanism, such as a rod, disposedlongitudinally of along the vehicle. Hence, it is preferable that thecontrol arm swing longitudinally around the lateral axis. Oneconventional construction is provided with a vertical operating shaft,independent of the trunnions, where both trunnions and the verticaloperating shaft interlock with each other. The control arm is providedat one end of the operating shaft so that the control arm swingslongitudinally around the vertical axis, and the other end isconstructed so that the trunnion projects at the axial end thereof fromthe front wall of the housing. A control arm is provided at the axialend so that the control arm swings laterally around the longitudinalaxis. A complex linkage mechanism, with respect to the verticaloperating shaft and trunnions, is required in the first constructiondescribed above, thereby increasing the number of parts and assemblytime, making the axle driving apparatus too expensive to produce. Thesecond construction described above requires a separate link mechanismfor converting the longitudinal motion into a lateral motion, therebyrequiring space to provide two link mechanisms in the vehicle, making itdifficult to apply the apparatus to a vehicle of small size andincreasing the number of parts required.

U.S. Pat. Nos. 5,440,951 and 5,515,747 disclose that when the HST andthe mechanism for transmitting power to the axles from the HST arehoused in the same housing, the housing can be filled with oil to beused as both operating oil for the HST and lubricating oil for thetransmitting mechanism. In this case, a foreign object, such as ironpowder, created by the rubbing of the transmitting mechanism may flowtoward the HST. The iron powder or other foreign object is removed by anoil filter so as not to enter into the HST closed fluid circuit.However, the iron powder or the like may encroach on the piston andswash plate and thereby adversely affect them. The housing is integratedin part with the oil reservoir so as to enable the oil volume in thehousing to be adjusted when expanded due to a rise in temperature.However, the greater the quantity of oil, the larger the increase involume. Thus, the housing must be made larger and the reservoirtherefore becomes larger so that the housing itself has to be large insize.

U.S. Pat. No. 5,094,077 discloses that in order to prevent the speedchange controller equipped on the vehicle from being hastily operated byan operator, a shock absorber is provided on the control arm. The shockabsorber should be disposed above the upper wall of the housing becausethe control arm is configured to vertically and longitudinally swingaround the axis on the upper wall of the housing. Therefore, space fordisposing the shock absorber without interference with an input pulleyor an enlarged portion of the upper wall of the housing is required.

Further, where a differential gear is provided between the left andright axles, when one axle is idling, a driving force cannot betransmitted to the other axle. Hence, it is desired to provide adifferential locking device on the axle driving apparatus forintegrating the differential locking device with the HST and the axles.

SUMMARY OF THE INVENTION

The axle driving apparatus of the present invention is partitioned by aninternal wall provided within the housing, into a first chamber forhousing therein the HST and a second chamber for housing therein axlesand a transmitting mechanism which transmits power from an output shaftof the HST to the axles. Both chambers are filled with common oil. Anoil filter is disposed therebetween to allow the chambers to communicatewith each other. One chamber communicates with an oil reservoir.Trunnions for the swash plate to change the output rotation of the HSTare supported between the internal wall and a side plate fixed to thehousing. The trunnions are disposed laterally of and in parallel to theaxles. One of the trunnions projects outwardly from the housing so as tofix an arm. The shock absorber is connected thereto, thereby preventinghasty speed change. A differential locking device is attached to adifferential gear differentially connecting the left and right axles.During the normal running of the vehicle, the differential rotation canbe performed. When one axle is idling, both axles are adapted to bedirectly connected to each other.

These and other objects of the invention will become more apparent fromthe detailed description and examples which follow.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a plan view of an axle driving apparatus;

FIG. 2 is a partially sectional plan view of the same in which an upperhalf housing thereof is removed;

FIG. 3 is a sectional view looking in the direction of arrows 3—3 inFIG. 2;

FIG. 4 is a sectional view looking in the direction of arrows 4—4 inFIG. 2;

FIG. 5 is a sectional view looking in the direction of arrows 5—5 inFIG. 2;

FIG. 6 is a sectional view looking in the direction of arrows 6—6 inFIG. 2;

FIG. 7 is a sectional view looking in the direction of arrows 7—7 inFIG. 2;

FIG. 8 is an enlarged sectional plan view of a principal portion of themechanism of a braking device;

FIG. 9 is an enlarged sectional side view of a principal portion of thesame;

FIG. 10 is a enlarged sectional view of only a part of a principalportion of the same;

FIG. 11 is a left side view of a center section of the presentinvention;

FIG. 12 is a plan view of the same;

FIG. 13 is a sectional view looking in the direction of arrows 13—13 inFIG. 11;

FIG. 14 a sectional view looking in the direction of arrows 14—14 inFIG. 11;

FIG. 15 is a sectional view looking in the direction of arrows 15—15 inFIG. 11;

FIG. 16 is a sectional view looking in the direction of arrows 16—16 inFIG. 12;

FIG. 17 is a sectional view looking in the direction of the arrows 17—17in FIG. 12;

FIG. 18 is a sectional view looking in the direction of the arrows 18—18in FIG. 12;

FIG. 19 is a sectional view looking in the direction of the arrows 19—19in FIG. 12;

FIG. 20 is a sectional view looking in the direction of the arrows 20—20in FIG. 12;

FIG. 21 is a bottom plan view of the center section from which thecharge pump has been removed;

FIG. 22 is sectional view of a differential gear and a differentiallocking device;

FIG. 23 is a side view of a slider of the differential locking device;

FIG. 24 is a side view of a ring gear of the same; and

FIG. 25 is a perspective exploded view of the differential gear of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-7 show the construction of an axle driving apparatus. Thehousing of the axle driving apparatus comprises an upper half housing 1and a lower half housing 2 joined to each other along a horizontal, flatjoint surface along the periphery of the upper and lower half housings1,2. A bearing for a motor shaft 4 is provided on the joint surfaces ofboth upper half housing 1 and lower half housing 2. Bearings for axles 7are shifted upwardly from the joint surface of both upper half housing 1and lower half housing 2 and are disposed in upper half housing 1 torotatably support axles 7. Axles 7 are differentially connected by adifferential gear unit 23 and project laterally outwardly of thehousing.

The interior of the housing is partitioned by an internal wall 8 into afirst chamber R1 for housing therein an HST and a second chamber R2 forhousing therein a gear-type drive train which transmits power todifferential gear unit 23 from motor shaft 4 to axles 7. First chamberR1 and second chamber R2 are filled with common oil which forms an oilsump. As shown in FIG. 7, an oil feed lid 6 is provided on an upper wallof upper half housing 1 above differential gear unit 23. The housing canbe filled with operating oil through lid 6. As shown in FIG. 6, an oilflow port 75 is provided in the upper portion of upper half housing 1.Upper half housing 1 communicates through a piping 9, of rubber hose orthe like, with the interior of an oil reservoir 10 mounted at apredetermined position on the vehicle, thereby enabling the volume ofoperating oil in oil reservoir 10 to be adjusted.

As shown in FIG. 6, an oil bore 8a is open at a predetermined positionin internal wall 8 which partitions first chamber R1 from second chamberR2. An oil filter 18 covers oil bore 8a. In this embodiment, as shown inFIGS. 2 and 6, oil bore 8a and oil filter 18 are disposed on internalwall 8 between the portion containing the HST and the portion containingthe right side axle 7, thereby enabling oil to flow between firstchamber R1 and second chamber R2 through oil filter 18. Accordingly, oilfilling the housing can be used as both operating oil for the HST andlubricating oil for the gears and bearings. When the oil enters intofirst chamber R1 from second chamber R2, foreign objects such as ironpowder which are harmful to the HST, are filtered by oil filter 18.

Internal wall 8 is provided within the housing so that first chamber R1is disposed in front of axles 7 and to the side of the drive train fortransmitting power from motor shaft 4 to differential gear unit 23.Internal wall 8, as shown in FIG. 4, comprises (1) an internal wallportion 1a erected integrally with the upper inner surface of upper halfhousing 1 and is positioned at the end surface on the same plane as thejoint surface of the housing parts 1, 2 and (2) an internal wall portion2a erected integrally with the inner bottom surface of lower halfhousing 2 and positioned at the end surface on the same plane as thejoint surface of the housing. When both upper half housing 1 and lowerhalf housing 2 are joined together, the end surfaces of both internalwall portion 1a and internal wall portion 2a join each other to forminternal wall 8, thereby partitioning the interior of the housing intofirst chamber R1 and second chamber R2.

The HST is housed in first chamber R1. The HST comprises a hydraulicpump P, a hydraulic motor M and a center section 5. Center section 5 iselongated and is longitudinally disposed in first chamber R1. A verticalsurface 91 is formed at the front of center section 5 on which hydraulicmotor M is disposed. A horizontal surface 90 is formed along the top ofcenter section 5 on which hydraulic pump P is disposed. A pump shaft 3is substantially vertically disposed on center portion section 5 and ispositioned between motor shaft 4 and axles 7 which extend substantiallyhorizontally and in parallel to each other. A pump mounting surface 40is formed on horizontal surface 90 of center section 5 for hydraulicpump P. A cylinder block 16 is rotatably and slidably disposed on pumpmounting surface 40. Pistons 12 are fitted into a plurality of cylinderbores in cylinder block 16 and are reciprocally movable by biasingsprings. The heads of pistons 12 abut against a thrust bearing 11a heldto the movable swash plate 11. At the center of movable swash plate 11,an opening 11b is provided through which pump shaft 3 perforates. Pumpshaft 3, used also as an input shaft, is disposed on the rotary axis ofcylinder block 16 and is fixed thereto as that the pump shaft 3 andcylinder block 16 rotate together. Pump shaft 3 projects at the upperaxial end thereof outwardly from the upper wall of upper half housing 1.An input pulley 43 with a cooling fan 44 is fixed to pump shaft 3. Inputpulley 43 is given power from a prime mover (not shown) through a belttransmitting mechanism (not shown).

As seen in FIG. 6, the piston abutting surface of movable swash plate 11is disposed perpendicular to the rotary axis of cylinder block 16.Movable swash plate 11 is shown in the neutral position. Movable swashplate 11 can be tilted from side to side so as to enable the dischargeamount and discharge direction of oil from hydraulic pump P to bechanged. As seen in FIG. 4, for example, movable swash plate 11 isintegrally provided with trunnions 35L and 35R, which project laterallyfrom both sides of swash plate 11 and are disposed in parallel to axles7. Movable swash plate 11, as shown in FIGS. 2 and 4, is slantinglyrotatably supported between the two parallel walls of internal wallportion 1a in upper half housing 1 and the side wall of the upper halfhousing 1. A recess 1b is bored in the side surface of internal wallportion 1a. Recess 16 has an inner diameter about equal to the outerdiameter of a bearing bush fitted on trunnion 35L. As best seen in FIG.4, trunnion 35L is rotatably supported in recess 1b. In order to borerecess 1b in internal wall portion 1a, an opening 1c is formed in theside wall of upper half housing 1. A machining tool for boring recess 1bis inserted into upper half housing 1 through opening 1c. A side plate15 for closing opening 1c is detachably fixed onto the outer surface ofthe side wall of upper half housing 1 through sealing members (notshown). Trunnion 35R extends into a hollow cylindrical portionintegrally formed in side plate 15 so as to be rotatably supportedtherein. Movable swash plate 11 is longitudinally tilted aroundtrunnions 35L and 35R within first chamber R1, enabling the output ofhydraulic pump P to be changed.

At the outer surface of side plate 15, a plurality of fins 15a (see FIG.3) for receiving cooling wind from cooling fan 44 are disposed in thedirection of the flow of the cooling wind. Wind blowing across fan fins15a lowers the temperature of oil stored in first chamber R1.

The axial end of trunnion 35R projects outwardly from side plate 15. Acontrol arm 38 (discussed below) is fixed onto the axial end and isconnected through a link or wire (not shown), to a speed change levermounted at the driver's seat of the vehicle, so as to rotate around thelateral axis of the vehicle body. This simplifies the transmittingmechanism for slantwise control of movable swash plate 11. A neutralreturn coiled spring 31 is fitted onto trunnion 35R in first chamber R1.Both ends of neutral return coiled spring 31 project forwardly betweenan engaging pin 39 and around an eccentric shaft 33 mounted onto theinner surface of side plate 15 (see FIG. 2). Engaging pin 39 projectsfrom an arm 11d which projects forwardly from movable swash plate 11.

Accordingly, when control arm 38 is rotated in order to change the speedof the vehicle, arm 11d rotates together therewith and one end ofneutral return coiled spring 31 moves away from the other end towardengaging pin 39. The other end of neutral return coiled spring 31 isretained by eccentric shaft 33 so as to apply a biasing force to controlarm 38 which tends to return to the neutral position. When the operatingforce to the speed change lever is released, the restoring force createdat one end of neutral return coiled spring 31 returns engaging pin 39toward eccentric shaft 33 so as to be held in a neutral position. Aportion of eccentric shaft 33 extending outwardly from side plate 15 isfixed thereto through an adjusting nut 33a, which can be released toproperly rotatably shift eccentric shaft 33, thereby shifting arm 11daround trunnion 35R through neutral return coiled spring 31. Thisenables movable swash plate 11 to be adjusted to the accurate neutralposition.

Control arm 38 is fixed to the end of trunnion 35R which extends outsideof the housing, as shown in FIG. 3. Control arm 38 is substantiallyV-shaped, with a first retaining portion 38a and a second retainingportion 38b. First retaining portion 38a projects upwardly to connectwith a speed changing member such as a lever or pedal (not shown), andwith trunnion 35R when the speed change force is applied. Secondretaining portion 38b projects slantwise rearwardly of the vehicle toconnect with one end of a movable portion 73a of a shock absorber 73.Shock absorber 73 and control arm 38 are formed to straddle right axle7. The base of a fixed portion 73b of shock absorber 73 is pivotallysupported to a mounting pin 74b. Mounting Pin 74b is mounted to the rearend of a support plate 74 fixed through mounting bolts 74a to the lowersurface of a sleeve for right axle 7. Thus, shock absorber 73 connectswith control arm 38 so as to prevent a rapid speed change operation.Further, the operating force of the speed changing member, whenreleased, does not rapidly return swash plate 11 to its neutralposition, due to the spring force of neutral return coiled spring 31.This prevents an abrupt stop of the vehicle caused by the braking actionof the HST.

Because shock absorber 73 is disposed longitudinally along one side ofthe housing, it is not necessary to consider the height of input pulley43 or an enlarged portion of the housing. A reasonable connection andarrangement is provided allowing control arm 38 to be swung along alateral axis of the apparatus.

Pressure oil from hydraulic pump P is sent to hydraulic motor M throughan oil passage in center section 5. Hydraulic motor M, as shown in FIG.5, is constructed so that a motor mounting surface 41 is formed alongvertical surface 91 of center section 5. A cylinder block 17 isrotatably slidably mounted to motor mounting surface 41. A plurality ofpistons 13 are reciprocally movably inserted into a plurality ofcylinder bores in cylinder block 17 through biasing springs. A thrustbearing, held to a fixed swash plate 37, abuts against the heads ofpistons 13. Fixed swash plate 37 is fixedly positioned between upperhalf housing 1 and lower half housing 2. Motor shaft 4 is disposed onthe rotary axis of cylinder block 17 and is fixed thereto so that motorshaft 4 and cylinder block 17 move together. One end of motor shaft 4 issupported in a shaft bore provided at the center of motor mountingsurface 41 of center section 5. The other end of motor shaft 4perforates through internal wall 8, formed at the joint surface of upperhalf housing 1 and lower half housing 2, so as to enter into secondchamber 2. Motor shaft 4 is rotatably supported by a bearing 76 fittedinto internal wall 8. Bearing 76 includes an oil-tight seal in order topartition first chamber R1 and second chamber R2. In particular, anO-ring 77 is provided on the outer periphery of bearing 76.

A brake disc 19 is fixed to one axial end of motor shaft 4 positioned insecond chamber R2. As shown in FIG. 9 a brake pad 98 is fitted into theinner surface of upper half housing 1 positioned at one side of theupper portion of brake disc 19. At the opposite side of brake disc 19, abrake operating shaft 97 is supported which perforates the wall of upperhalf housing 1 from the outside to the inside thereof through a supportplate 92. Brake pad 98 and the end surface of brake operating shaft 97are opposite to each other. Brake disc 19 is sandwiched therebetween.Brake operating shaft 97 is supported in parallel to motor shaft 4. Abrake arm 93 is fixed to the end of brake operating shaft 97 outside ofthe housing. A spring 94 is fitted onto brake operating shaft 97 betweenbrake arm 93 and support plate 92, so as to bias the end surface ofbrake operating shaft 97 away from brake disc 19.

A flange 97a is formed within the housing at one end of brake operatingshaft 97. A plurality (four in this embodiment) of groves grooves 97bare provided at the surface of flange 97a facing the inner surface ofthe housing. Cam grooves 92a, each V-shaped in cross-section and arcuatewhen viewed in plan are provided at the end surface of support plate 92,opposite to grooves 97b. As shown in FIG. 10, balls 95 are interposedbetween cam grooves 92a and grooves 97b. In such construction, whenbrake arm 93 is rotated, brake operating shaft 97 rotates along itslongitudinal axis. Balls 95, held by recesses 97b, slowly ride onto theshallowest portions of cam groove 92a from the deepest portions thereof.This causes brake operating shaft 97 to slidably move, due to the thrustgenerated thereon by balls 95, toward brake disc 19 thereby sandwichingbrake disc 19 between brake pad 98 and the end surface of brakeoperating shaft 97 so as to brake motor shaft 4. Flanges 92b, whichextend radially and are V-shaped, are integrally provided at the outerend of support plate 92 (see FIG. 8). Elongate slots 92c, which areoval-arcuate shaped are open in flanges 92b around brake operating shaft97. Bolts 96 are inserted into elongate slots 92c, thereby fixingsupport plate 92 onto the outer surface of the side wall of upper halfhousing 1. Bolts 96 may be unscrewed to properly rotate flanges 92baround brake operating shaft 97, thereby enabling balls 95 to adjust thelength of time during which balls 95 ride on cam groove 97b.

Next, explanation will be given on the construction of center section 5for loading thereon hydraulic pump P and hydraulic motor M in accordancewith FIGS. 11 through 21. Center section 5 is longitudinally elongatedand is provided at one side thereof with a bolt bore 5h and at anotherside thereof with two bolt bores 5h. Three mounting bolts are insertedinto bolt bores 5h and are used to fix center section 5 to the innerwall of upper half housing 1 in first chamber R1. At the center of pumpmounting surface 40 and at the rear and upper surface of upper halfhousing 1 is formed a bearing bore for rotatably supporting the lowerend of pump shaft 3. A pair of arcuate ports 40a and 40b are openlongitudinally through center section 5 around a bearing bore. Feed ordischarge oil is communicated with cylinder block 16 through parts ports40a and 40b. At the center of motor mounting surface 41, verticallydisposed in front of pump mounting surface 40, is bored a bearing borefor rotatably supporting one end of motor shaft 4. A pair of arcuateports 41a and 41b are open vertically and around the bearing bore,thereby communicating feed or discharge oil with cylinder block 17.

In order to connect arcuate ports 40a and 40b at pump mounting surface40 with arcuate ports 41a and 41b at motor mounting surface 41, a firstlinear oil passage 5a and a second linear oil passage 5b are bored in athick portion of center section 5, in parallel to each other. As shownin FIG. 12, the center of pump mounting surface 40 is positioned alongan imaginary vertical plane (line 16—16) disposed along motor mountingsurface 41. Half of cylinder block 16 mounted on pump mounting surface40 (as shown in FIG. 2) overlaps, when viewed from above, with half ofcylinder block 17 disposed on motor mounting surface 41. Thisarrangement permits the HST and first chamber R1 which contains the HSTto be smaller in lateral width. A third linear oil passage 5ccommunicates horizontally and perpendicularly with an intermediateportion of second oil passage 5b. Arcuate port 40a at pump mountingsurface 40, as shown in FIG. 18, is shallow and directly communicateswith first oil passage 5a. Arcuate port 40b is deeper to communicatewith third oil passage 5c. Arcuate port 41a at motor mounting surface 41is deeper at the upper portion thereof to communicate with first oilpassage 5a and shallow at the lower portion thereof, as shown in FIGS.16 and 17. Arcuate port 41b communicates, at the lower portion thereof,with second oil passage 5b. Thus, first oil passage 5a communicates witharcuate port 40a and with arcuate port 41a, while second oil passage 5band third oil passage 5c communicate with arcuate port 40b and witharcuate port 41b, so as to form a closed fluid circuit in center section5.

With reference to FIG. 17, check valves 54 and 55 are disposed at theopen ends of first oil passage 5a and second oil passage 5brespectively. Both first oil passage 5a and second oil passage 5b areclosed by plug members 64a in which check valves 54 and 55 are disposed,respectively. The open end of third oil passage 5c is closed by a plugmember 64b. Check valves 54 and 55 communicate at the inlet sidesthereof with oil passage 5d through oil bores 54b and 55b provided atcasings 54a and 55a. The open end of oil passage 5d is positioned in arecess 5g formed at the lower surface of center section 5. At the lowersurface of center section 5, opposite to pump mounting surface 40, acharge pump casing 46 is mounted through a plurality of mounting bolts69. A trochoid-type charge pump 45 is housed (see FIG. 4) in a recessformed at a center of the is upper surface of charge pump casing 46.Trochoid-type charge pump 45 is provided with internal teeth andexternal teeth. The lower end of pump shaft 3 projects downwardly fromcenter section 5 and engages with the external teeth so as to drivecharge pump 45. Charge pump 45, however, may be of an external gear typeor other known type.

As seen in FIGS. 18 and 19, charge pump 45 has a discharge port 45a andan intake port 45b. Intake port 45b communicates with an opening 46b(FIG. 17) into which the open end of a cylindrical oil filter 56 isinserted (see FIGS. 5 and 6). Oil filter 56 is disposed under hydraulicmotor M in first chamber R1. Oil filter 56 is insertable into chargepump casing 46 which is in the housing from the exterior thereof throughan insertion bore open at the front wall of lower half housing 2. Oilfilter 56 is interposed between charge pump casing 46 and a plug member48 which closes the insertion bore at the front wall of lower halfhousing 2. Plug member 48 can be removed to facilitate maintenance andinspection of oil filter 56. A pair of oil joints 49 and 50 project fromthe a side surface of charge pump casing 46 (FIG. 13). The ends ofjoints 49 and 50, as shown in FIG. 3, are exposed at a lower portion ofthe outside surface of lower half housing 2. Oil joints 49 and 50function as an oil pressure source for hydraulic actuators equippedoutside of the vehicle.

Oil joint 50 is formed to serve as an oil takeout port and communicateswith discharge port 45a of charge pump 45 through an oil passage 46a asshown in FIG. 13. A first relief valve 57, for setting the oil pressureof discharge port 45a, is housed in charge pump casing 46 and isconnected to an oil passage 46c which is branched from oil passage 46a.Relief oil discharged from first relief valve 57 flows into recess 5g atthe lower surface of center section 5 through oil passage 46c. Oil joint49 is formed to be an oil return port and to communicate with recess 59of center section 5 through oil passages 46d and 46e. A second reliefvalve 58 for setting the oil pressure in recess 5g to be supplied to theclosed circuit of the HST is housed in charge pump casing 46 andconnects with recess 5g through an oil passage 46f. Relief oildischarged from second relief valve 58 is discharged outwardly fromcharge pump casing 46 through an oil passage 46g.

As seen in FIG. 17, when charge pump 45 is driven, oil flowing intorecess 5g through the oil passage 46c is adjusted by second relief valve58. This causes check valve 54 or 55 to open through oil passage 5d atthe low pressure side of one of oil passages 5a, 5b or 5c, therebyforcibly supplying operating oil into the closed fluid circuit for theHST.

When the vehicle is stopped on a sloping surface, and the HST is put inthe neutral position without the parking brake exerted, the forcecausing the driving wheels of the vehicle to roll acts on the closedfluid circuit of the HST to generate pressure so as to cause negativepressure in the closed fluid circuit and possibly causing the vehicle tomove. In order to prevent such a phenomenon, a check valve 47 (see FIG.15) is housed in charge pump casing 46 which can supply operating oil tothe closed fluid circuit of the HST even when charge pump 45 is notdriven. Check valve 47 communicates at the inlet side thereof withintake port 45bthrough an oil passage 46h and at the outlet side withrecess 5g through an oil passage 46i. When charge pump 45 is driven toflow operating oil into recess 5g though oil passages 46c and 46e, checkvalve 47 closes between oil passage 46h and oil passage 46i. When chargepump 45 is not driven, causing negative pressure on the low pressureside of the closed circuit, check valve 47 is open to enable oilfiltered by filter 56 to be guided from intake port 45band oil passages46h and 46i into recess 5g. Check valve 54 or 55, at the negativepressure side of the closed fluid circuit, is open through oil passage5d, whereby oil is supplied to the closed fluid circuit. Thus, oil canbe maintained in the closed fluid circuit at all times.

In order to place operating oil into the closed fluid circuit after theaxle driving apparatus is assembled, oiling pipes 52 and 53 are disposedat the lower surface of center section 5 as shown in FIGS. 11, 15, 17and 20. At the lower surface of center section 5, a fourth verticalpassage 5e is bored to communicate with the upper deep portion ofarcuate port 41a A fifth vertical oil passage 5f is bored to communicatewith second oil passage 5b. Oiling pipes 52 and 53 are mounted into oilpassages 5e and 5f respectively and are opened at the lower ends thereofoutwardly from the bottom wall of lower half housing 2 and closed at theopen ends by use of plug members after the closed fluid circuit isfilled with operating oil.

As shown in FIGS. 2 and 5, a by-pass arm 60 for opening the interior ofthe closed circuit to the oil sump, in order to enable the axle to beidle during hauling of the vehicle, is disposed in the upper portion ofupper half housing 1. In particular, by-pass arm 60 is fixed at its baseonto the upper end of a by-pass shaft 61, which is vertically, rotatablyand pivotally supported to the upper wall of upper half housing 1.By-pass shaft 61 extends at its lower end into a thick portion of motormounting portion 41 of center section 5. A flat surface 61a is formed ata part of the outer periphery of the lower end of by-pass shaft 61. Athrough-bore 5i (see FIG. 11) is open at motor mounting surface 41 ofcenter section 5 slightly above the center thereof and between arcuateport 41a and 41b. A push pin 62 (see FIG. 5) is slidably supported intothrough-bore 5i along the rotary axis of cylinder block 17. One endsurface of push pin 62 can abut against the rotary sliding surface ofcylinder block 17 in close contact with the motor mounting surface 41.The other end surface abuts against flat surface 61a of by-pass shaft61.

Thus, when an operator operates a by-pass operating lever (not shown)equipped on the vehicle when the vehicle is hauled, by-pass shaft 61 isrotated through by-pass arm 60. Push pin 62 is pushed toward cylinderblock 17 by the flat surface of the lower end of by-pass shaft 61. Pushpin 62 moves the cylinder block 17 above motor mounting surface 41.First oil passage 5a and second oil passage 5b communicate with the oilsump of the housing through arcuate ports 41a and 41b respectively,thereby enabling motor shaft 4 to freely rotate.

As shown in FIGS. 2 and 7, the drive train for transmitting power frommotor shaft 4 to differential gear 23 is constructed with a gear 25provided on a portion of motor shaft 4 entering into second chamber R2,for engaging with a larger diameter gear 24, fixed onto a counter shaft26. A smaller diameter gear 21 is also fixed onto counter shaft 26 andengages with an input gear 22. Power from motor shaft 4 is reduced inspeed by gears 25, 24 and 21 to drive differential gear unit 23 by inputgear 22. Larger diameter gear 24, on counter shaft 26, is disposed tothe side of input gear 22 and overlaps in part therewith. Counter shaft26 is rotatably housed in lower half housing 2 and is supported at bothaxial ends in a recess formed on the side wall of lower half housing 2and a recess formed on the internal wall 2a of lower half housing 2, asshown in FIG. 2, so as to be rotatably supported when lower half housing2 is joined with upper half housing 1.

As best seen in FIGS. 2 and 22, the distal ends of axles 7 are rotatablysupported by ball bearings in axle housing portions projecting fromupper half housing 1. The proximate end of each axles 7 is sleeved by abearing bush. One half of each bearing bush is received in a recess inupper half housing 1. The other half is received by a projection oflower half housing 2 which enters into upper half housing 1. Axles 7 arerotatably supported to receive power transmitted through differentialgear 23. As shown in FIG. 2, the HST is disposed to the right side ofthe drive train. A control arm 38 for movable swash plate 11 is disposedto the right side of the HST. Hydraulic pump P is positionedsubstantially at the lateral and longitudinal center of the apparatusand is disposed so as to avoid the enlarged portion of differential gear23. This enables the housing to be compact.

Differential gear unit 23 is shown in FIGS. 22 through 25. As seen inFIG. 24, the center of input gear 22 has a shaft bore 22a for receivingaxles 7 therein. Bores 22b for receiving differential pinions 80 andfitting-in bores 22a for receiving the differential locking device aredisposed at both sides of input gear 22. Spline-fitted bevel-type outputgears 81L and 81R are disposed at the proximate end of axles 7. Spindles80a of the bevel-type differential pinions 80 are retained in bores 22bof input gear 22 in which differential pinions 80 are also housed.Differential pinions 80 engage with output gears 81L and 81R so as toform differential gear unit 23. No differential casing is otherwiseprovided. The differential locking device is provided opposite to thedrive train at one side (preferably the right side) of differential gear23 unit.

Between output gear 81R and the proximate end of right axle 7 isinterposed a collar 83 on which a slider 82 is axially slidably fitted.Slider 82 is cup-like shaped to wrap around output gear 81R. At theouter peripheral side surface of slider 82, projections 82a areintegrally provided. Projections 82a are permanently engageable withinsertion bores 22c of input gear 22. At the inner peripheral sidesurface of slider 82 are formed a plurality of projections 82b which areengageable with a plurality of recesses 81a formed in the outerperiphery of output gear 81R. An insertion groove 82c is formed on thecylindrical portion of slider 82 opposite to projections 82a, so as tofit the tip of a fork 84 into groove 82. The base of fork 84 is slidablyfitted onto a shaft 85 which is journalled to both side walls in lowerhalf housing 2. At the side surface of the base of fork 84 is formed acam surface 84a, which abuts against a pin 87 provided on shaft 85 so asto constitute a cam mechanism. An arm 86 is fixed to shaft 85. Arm 86projects outwardly from the housing so as to connect with a differentiallocking pedal (not shown) provided on the vehicle.

In such construction, when the operator presses the differential lockingpedal, shaft 85 rotates through arm 86, and pin 87 rotates to push tothe right in the drawing of FIG. 22. As a result, cam surface 84a abutsagainst pin 87 so as to slidably move fork 84. At the same time, slider82 slides, while maintaining projections 82a in insertion bores 22c ofring gear 22. Projections 82b engage with recesses 81a of output gear81R and input gear 22 is differentially locked and coupled with axles 7.As a result, axles 7 are uniformly driven when the vehicle runs on anyroad surface.

The axle driving apparatus of the present invention can be used fordriving the axles of a vehicle to improve the operability of changingthe speed of the vehicle. An example of a moving vehicle which mayutilize the above-mentioned axle driving apparatus is a farm or otherworking vehicle, such as a tractor with a mower attachment, or othervehicle for transportation.

While one embodiment of the present invention has been shown anddescribed, the invention should not be limited to the specificconstruction thereof, and is meant to be merely exemplary.

1. An axle driving apparatus for a vehicle, comprising; a housing; anaxle disposed in said housing; an input means disposed in said housing;a hydraulic pump driven by said input means, wherein said hydraulic pumpis provided with a reciprocally movable cylinder block with a pluralityof pistons disposed in said cylinder block, said cylinder block having arotary axis which is substantially perpendicular to a rotary axis ofsaid axle; a movable swash plate for receiving thrust from the heads ofsaid pistons; means disposed on opposite sides of said movable swashplate in said housing for rotatably supporting said movable swash plateand for permitting said movable swash plate to slant along an axissubstantially parallel to said axle, said means for rotatably supportingsaid movable swash plate includes a first trunnion provided at one sideof said swash plate having an axis which coincides with a slantinglyrotary axis of said swash plate and extends outwardly from a side wallof said housing, and an arm fixed to the outer end of said firsttrunnion connected with a speed change operating member provided on saidvehicle which longitudinally, swingably moves around said slantinglyrotary axis; a hydraulic motor driven by pressurized oil from saidhydraulic pump; an output means driven by said hydraulic motor; a drivetrain for drivingly connecting said output means and said axles; and ashock absorber mounted between said arm and said housing for applyingoperational resistance to said speed change operating member.
 2. An axledriving apparatus for a vehicle, comprising: a housing; an axle disposedin said housing; an input means disposed in said housing; a hydraulicpump disposed in said housing and driven by said input means, whereinsaid hydraulic pump is provided with a reciprocally movable cylinderblock with a plurality of pistons disposed in said cylinder block, saidcylinder block having a rotary axis which is substantially perpendicularto a rotary axis of said axle; a movable swash plate for receivingthrust from the heads of said pistons; means disposed on opposite sidesof said movable swash plate in said housing for rotatably supportingsaid movable swash plate and for permitting said movable swash plate toslant along an axis substantially parallel to said axle, said meansincluding a pair of first and second coaxial trunnions provided atrespective opposite sides of said swash plate, said pair of trunnionshaving axes coinciding with a slantingly rotary axis of said swashplate; a hydraulic motor disposed in said housing and driven bypressurized oil from said hydraulic pump, wherein said hydraulic pump,wherein said hydraulic pump is located between said axle and saidhydraulic motor when viewed in plan; an output means driven by saidhydraulic motor; a drive train for drivingly connecting said outputmeans and said axle, said drive train having a shaft; and a partitionwall formed in said housing, said hydraulic pump and said hydraulicmotor being disposed at one side of said partition wall, said drivetrain being disposed at an other side of said partition wall, whereinone end of said shaft of said drive train is supported by said one sideof said partition wall, and wherein said first trunnion is supported bysaid other side of said partition wall.
 3. An axle driving apparatus fora vehicle according to claim 2, wherein said housing is provided with afirst housing member and a second housing member joined along a planesubstantially perpendicular to said rotary axis of said cylinder block,and wherein said movable swash plate is slantingly movably housed insaid first housing member.
 4. An axle driving apparatus for a vehicleaccording to claim 2, wherein said second trunnion extends outwardlyfrom a side wall of said housing, and said means for rotatablysupporting said movable swash plate further includes: an arm fixed tothe outer end of said second trunnion connected with a speed changeoperating member provided on said vehicle which longitudinally swingablymoves around said slantingly rotary axis.
 5. An axle driving apparatusfor a vehicle according to claim 4, further comprising: a shock absorbermounted between said arm and said housing for applying operationalresistance to said speed change operating member.
 6. An axle drivingapparatus for a vehicle according to claim 4, further comprising: a sideplate mounted on one side wall of said first housing member forsupporting said first trunnion; and a bias mechanism disposed betweensaid side plate and said movable swash plate for returning said movableswash plate to a neutral position.
 7. An axle driving apparatus for avehicle according to claim 6, further comprising: a cooling fan disposedabove said first housing member and integrally rotatable with said inputmeans; and a plurality of fins provided at an outer surface of said sideplate and disposed in the direction of the flow of cooling windgenerated by said cooling fan.
 8. An axle driving apparatus for avehicle comprising: a hydrostatic transmission including an input means,a hydraulic pump driven by said input means, a hydraulic motor driven bypressurized oil from raid said hydraulic pump, and an output meansdriven by said hydraulic motor; an axle; a drive train for connecting ina driving manner said output means of said hydrostatic transmission withsaid axle, wherein said output means, said drive train and said axlehave rotary axes in parallel to one another; and a housing containingsaid hydrostatic transmission, said axle, and said drive train, saidhousing being dividable into a first housing member and a second housingmember along a first plane perpendicular to said axle, wherein anopening surface defining said first plane is formed in each of saidfirst and second housing member members, and wherein a height of saidopening surface is larger than the greatest diameter largest radius ofsaid swash plate in rotation; wherein said hydraulic pump is providedwith a reciprocally movable cylinder block, containing therein aplurality of pistons and having a rotary axis substantiallyperpendicular to said rotary axis of said axle, a movable swash platefor receiving thrust from the heads of said pistons, and a means forslantingly rotatably supporting said movable awash swash plate in saidhousing; wherein said means for slantingly rotatably supporting saidmovable swash plate includes a first trunnion and a second trunnionprovided coaxially at respective opposite sides of said movable swashplate in , said first and second trunnions being substantially parallelto said axle, said first trunnion is being rotatably supported by saidfirst housing member and is extended extending outwardly from said firsthousing member to be fixed to an arm linked with a speed changing memberequipped on said vehicle, and said second trunnion is being rotatablysupported by said second housing member.
 9. An axle driving apparatusfor a vehicle according to claim 8, wherein a third housing member isseparably joined to said second housing member through a second planesubstantially perpendicular with respect to the rotary axis of saidcylinder block.
 10. An axle driving apparatus for a vehicle according toclaim 9, further comprising: a first internal wall portion formed withinsaid second housing member for supporting said second trunnion.
 11. Anaxle driving apparatus for a vehicle according to claim 10, furthercomprising: a second internal wall portion formed within said thirdhousing member; wherein end surfaces of said first internal wall portionand said second internal wall portion extend toward said second plane,overlapping each other when said second housing member and said thirdhousing member are joined and forming in amid housing a first sectionfor containing therein said hydrostatic transmission and a secondsection for containing therein said drive train.
 12. An axle drivingapparatus for a vehicle according to claim 11, further comprising: anintermediate transmitting member disposed between said output means andsaid axles, said intermediate transmitting member having a rotary axisextending substantially in parallel to said second plane; and a shaftfor disposing thereon said intermediate transmitting member, said shaftbeing sandwiched between said first internal wall portion and saidsecond internal wall portion for support.
 13. An axle driving apparatusfor a vehicle according to claim 7, further comprising: an internal wallportion formed within said second housing member for supporting saidsecond trunnion.